This invention relates, in general, to filter circuits, and more particularly, to spike filter circuits for receiving asynchronous data.
Digital data is typically transferred between a transmitter circuit and one or more receiver circuits. Synchronous data transmission requires a transmitter and a receiver circuit to be synchronized to one another to insure error free transmission. For some systems it may be difficult to synchronize transmitter and receiver circuits depending on the mode of transmission and the location of the receiver circuits.
Asynchronous data transmission simplifies the transmission of data but requires a receiver circuit capable of detecting when data is transmitted. Furthermore, the rejection of noise is critical to the integrity of transmitted data, noise must not be interpreted by a receiver circuit as data. Many error prevention techniques such as error correction codes or data protocols are implemented to minimize errors in asynchronous data transmission.
One common problem in the transmission of data is noise. Receiver circuits are designed to be sensitive to voltage changes that represent data. Thus receiver circuits are also sensitive to voltage changes produced by noise. For example, a noise spike is sometimes introduced to a stream of data due to capacitive coupling from one transmission line to another wherein a receiver circuit could interpret the noise spike as a data bit corrupting the entire stream of data. Noise spikes are also generated by common elements in the data environment such as a power surge or an electromagnetic pulse.
It would be of great benefit if a circuit could be developed that detects and filters out noise before being processed by a receiver circuit thereby reducing an error mechanism common to data transmission.